The present invention relates to telescoping lift arms that may be used for loader arms, either in pairs or as an individual, single boom, and which have a bell shaped cross section that permits an inner lift arm to slide or telescope relative to an outer lift arm and to be guided along linear bearings. The clearance of guide surfaces between inner lift arm and outer lift arm can be changed to adjust for wear without disassembly and replacement of the linear bearings.
Telescoping lift arms have been well known, and used in various applications, including front end loaders, crane booms, and the like. Various lift arm cross sections have been used for the telescoping lift arms, but the ability to adjust the fit or wear surface clearance of the sliding bearings or wear pads used after the bearings have fully seated, or have become worn, has been difficult. Replacement of bearings is usually necessary from time to time during use. This results in down time of the equipment, as well as extra expense for maintenance.
Rollers have been utilized for supporting the inner lift arm section, but rollers also become worn and are difficult to adjust.
The present invention relates to a telescoping lift arm assembly having inner and outer lift arm sections that are channel shaped and are formed so the inner section slidably nests in the outer section. The sliding arm channel have cross sections that flare out along the lower side edges. The lift arms thus have essentially xe2x80x9cbell shapedxe2x80x9d cross sections. The lower side of the inner telescoping lift arm is closed to form a tube that is supported relative to the lower edge portions of the outer lift arm sections only. There is clearance between the lift arm tubes at the top of the inner sections.
The flared lower wall portions of the inner lift arm tube have outer surfaces that are supported through linear bearings on complementary shaped inner surface portions of the outer lift arm section. The inner lift arm section is closed with a generally flat or planar bottom plate that is fixed in place and supported on an outer adjustable, and preferably removable lower plate forming the bottom wall of the outer lift arm tube.
The removable bottom plate of the outer lift arm tube can be adjustably clamped in place, with low coefficient linear bearing or wear pads between the bottom plates of the inner and outer lift arm tubes, and between the flared lower edge portions of the lift arm tubes. The linear bearings provide low friction, non binding support. The bottom plate of the outer lift arm tube will be moved toward the inner tube as it is tightened in place. Shims are used to positively position the outer lift arm bottom plate and permit tightening the adjusting bolts without directly affecting the load on the linear bearings.
The clearances of the linear bearings that are between guide surfaces of the inner and outer lift arm tubes can be adjusted. The adjustment of the bottom plate of the outer lift arm section can be made to compensate for wear on the linear bearings or wear pads.
The removable bottom plate or wall of the outer lift arm tube also makes assembly of the two nesting arm tubes easy, as well as permitting easy installation, adjustment and replacement of the linear bearings or wear pads. The outer adjustable and removable bottom plate permits the inner lift arm tube to be slipped up into the open bottom of the outer lift arm tube, and with the linear bearings also installed, the bottom plate is put into place and adjusted, preferably with shims, to provide the appropriate loading of the linear bearings between the two telescoping lift arm tubes.
The bottom plate wall may have notches on its edges, the side walls of the outer lift arm have inturned tabs that fit into the notches to positively position the bottom plate in longitudinal directin and to prevent it from moving with the inner lift arm when the inner lift arm tube telescopes.
The extension and retraction of the inner lift arm tube is done in a conventional manner with a double acting hydraulic cylinder connected between the two telescoping tubes and positioned within the lift arm tubes.